Puffy winter coats can cause harness issues. Take those winter coats off before you put your child in that harnessed car seat. You can put the coats back on them backwards once they are in the car.
The fluffy padding in those coats will compress in a crash, leaving extra space under the harness.
You can dress your child in thin layers or use a blanket over the harness straps to keep your child warm AND maintain proper car seat use in the winter.
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